What is orthostatic syncope?

Orthostatic Syncope: Definition, Mechanisms, and Management

Orthostatic syncope is a temporary loss of consciousness caused by cerebral hypoperfusion that occurs when assuming an upright position due to a significant drop in blood pressure without adequate compensatory mechanisms. 1

Types of Orthostatic Syncope

Classical Orthostatic Hypotension (OH)

• Defined as a sustained decrease in systolic BP ≥20 mmHg, diastolic BP ≥10 mmHg, or a sustained decrease in systolic BP to an absolute value <90 mmHg within 3 minutes of standing or head-up tilt 1
• In cases of supine hypertension, a systolic BP drop ≥30 mmHg should be considered significant 1
• Orthostatic heart rate increase is typically blunted (<10 bpm) in neurogenic OH due to impaired autonomic control 1
• Associated with increased mortality and cardiovascular disease prevalence 1

Initial Orthostatic Hypotension

• Characterized by a BP decrease on standing of >40 mmHg for systolic BP and/or >20 mmHg for diastolic BP within 15 seconds of standing 1
• BP spontaneously and rapidly returns to normal, with symptoms lasting <40 seconds 1
• More common in young, asthenic subjects and older adults, and can be drug-induced (particularly by alpha-blockers) 1

Delayed Orthostatic Hypotension

• Defined as OH occurring beyond 3 minutes of head-up tilt or active standing 1
• Characterized by a slow progressive decrease in BP 1
• The absence of bradycardia helps differentiate it from reflex syncope 1
• May induce reflex syncope due to decreased central blood volume 1
• Common in elderly persons, attributed to stiffer hearts and impaired compensatory vasoconstrictor reflexes 1

Clinical Presentation

Symptoms

• Dizziness, lightheadedness, weakness, fatigue, lethargy 1
• Palpitations, sweating, tremor 1
• Visual disturbances (blurring, enhanced brightness, tunnel vision) 1
• Hearing disturbances (impaired hearing, crackles, tinnitus) 1
• Pain in neck (occipital/paracervical and shoulder region), low back pain, or precordial pain 1
• Syncope (complete loss of consciousness) 1, 2

Timing of Symptoms

• Symptoms typically develop upon standing 1
• Are relieved by sitting or lying down 1
• May be worse in the morning, with heat exposure, after meals, or after exertion 1

Diagnostic Approach

• Active standing test: Measure BP and heart rate in supine position and after standing for 3 minutes 1, 3
• Head-up tilt testing: Recommended if active standing test is negative but history is suggestive of OH 3
• OH is diagnosed when there is a fall in systolic BP ≥20 mmHg and diastolic BP ≥10 mmHg within 3 minutes in upright position 3

Management

Non-Pharmacological Interventions

• Increase daily fluid intake to 2-3 liters 4
• Increase salt consumption (5-10g daily) 1, 4
• Avoid rapid postural changes 2, 5
• Physical counter-pressure maneuvers (leg-crossing, squatting, muscle tensing) 1, 4
• Compression garments (waist-high for optimal effect) 1, 4
• Elevation of the head of the bed during sleep 4
• Careful exercise to improve conditioning 6

Pharmacological Management

• First-line: Fludrocortisone for volume expansion in patients with hypovolemic OH 1, 4, 5
• Midodrine (2.5-10 mg three times daily) to enhance vascular tone, with first dose in morning before rising and last dose no later than 4 PM to avoid supine hypertension 4, 5
• Droxidopa can be beneficial in patients with syncope due to neurogenic OH 1
• Pyridostigmine may be beneficial in patients refractory to other treatments 1
• Octreotide may be beneficial in patients with refractory recurrent postprandial or neurogenic OH 1

Special Considerations

Medication Management

• Reduce or withdraw medications that may cause hypotension (vasoactive drugs and diuretics) 1, 4
• Monitor for supine hypertension with vasoconstrictors like midodrine 4
• Use midodrine with caution in older males due to potential urinary outflow issues 4

Elderly Patients

• More susceptible to OH due to age-related changes in cardiovascular system 5, 6
• May have impaired recovery of BP after initial fall, which represents a negative prognostic factor 1
• Often have comorbidities and polypharmacy that exacerbate OH 6

Acute Management

• Fluid resuscitation via oral or intravenous bolus for acute dehydration 1
• Physical counter-maneuvers during symptomatic episodes 1, 4

Distinguishing from Other Causes of Syncope

• Absence of bradycardia helps differentiate delayed OH from reflex syncope 1
• Timing of BP drop helps distinguish OH (immediate on standing) from vasovagal syncope (several minutes after standing) 1
• Orthostatic syncope must be differentiated from cardiac syncope, seizures, and other causes of loss of consciousness 7